Jatropha curcas L. is a multipupose shrub of significant economic importance because of its several potential industrial and medicinal uses. Jatropha curcas L. or physic nut (or purging nut) is a drought resistant large shrub or small tree, belonging to the genus Euphorbiaceae, producing oil containing seeds. The species has its natural distribution area in the Northeastern part of South America. (Heller, 1996) and central Africa and several countries in Asia. The seeds of physic nut are a good source of oil, which can be used as a diesel substitute. They are used also in medicines, and soap and cosmetics manufacture in various tropical countries.
The fruit of J. curcas is green/yellow when fresh and contains seed. The seed and seed products of J. curcas are potentially a source of high nutritional value, e.g., as animal feed. The levels of essential amino acids, except lysine, in the seed cake are higher than that of the FAO/WHO reference protein for a five year old child in all the meal samples on a dry matter basis. The major fatty acids found in the oil samples were oleic (41.5-48.8%), linoleic (34.6-44.4%), palmitic (10.5-13.0%) and stearic (2.3-2.8%) acids. The residual protein-rich seed cake, remaining after extraction of the oil, could form a protein-rich ingredient in feeds for poultry, pigs, cattle and even fish if it could be detoxified.
Like the oil, the seed cake is toxic and therefore only suitable as animal feed after processing. The toxicity of J. curcas is based on several components (phorbol esters, curcains, trypsin inhibitors and others) which make complete detoxification a complicated process. Detoxification has been successful at laboratory scale (Gross et al., 16 1997; Martinez Herrera et al., 2006), but since the process is complicated, it is not suitable for small scale and local use. Large scale feed production, however, has to compete on a global market with high quality demands. Therefore, detoxification must be complete, constant and guaranteed, and is thus expected to be expensive. Hence, a successful penetration of J. curcas seed cake as feed to the market at a profitable price seems doubtful.
Toxic components. The main toxic components are phorbol esters, although in Mexico accessions without, or with low content of phorbol esters have been found (Rivera Lorca & Ku Vera, 1997; Martinez Herrera et al., 2006; Basha & Sujatha, 2007). The seed cake of this so called ‘non’ or ‘low’ toxic variety might be suitable for use as animal feed, but it still contains minor quantities of toxic components and resistance on the feed market towards this product is to be expected.
On the other hand, the seed cake is nutrient rich and therefore very suitable as fertilizer (Table 3). Together with the fruit coats, the major part of the nutrients can be recycled. When no fertilizers are used, which is assumed to be the case in the use of J. curcas as a low input crop, this recycling is necessary to maintain soil fertility, especially on non fertile marginal lands. Patolia (2007a) reported total above ground dry matter increase of 24% after 2 years.
Because of unavoidable inefficiencies, recycling nutrients will only be effective at a certain production level that allows a high dynamic nutrient cycle to take place. Initiating a plantation on low or non fertile soils therefore implies the need to use other fertilizers, at least at the start, to boost crop growth and seed production in the initial stages. The harvested part of J. curcas is the fruit, mostly containing three seeds. The seeds make up about 70% of the total weight of the fruit (30% fruit coat); the mature fruits have amoisture content of circa 15%, the seeds circa 7%. The oil is stored in the interior of the seed: the kernel, which makes up circa 65% of the total mass of the seed. The moisture contents are circa 10% for the hull and circa 5% for the kernel.
Oil fraction and quality. The seed of J. curcas contains a viscous oil, highly suitable for cooking and lighting by itself and for the production of biodiesel. The total fraction of oil, fats and carbohydrates is circa 30 to 35% for the seed and, since 99% of the oil is stored in the kernel, circa 50 to 55% for the kernel (Table 1).
The oil contains very little other components and has a very good quality for burning. Cetane number of J. curcas oil (23-41) is close to cottonseed (35-40) and better than rapeseed (30-36), groundnut (30-41) and sunflower (29-37) (Vaitilingom & Liennard, 1997). The toxicity of J. curcas is mainly based on phorbol esters and curcains, which give no pollution when burnt. The oil is also very suitable for transesterification into biodiesel (Mohibbe Azam et al., 2005).
The absence of sulphur dioxide (SO2) in exhaust from diesel engines run on J. curcas oil shows that the oil may have a less adverse impact on the environment (Kandpal & Madan, 1995). As J. curcas oil has a higher viscosity than diesel oil (53 versus 8 cSt at 30 C), blending J. curcas oil up to 50% with diesel oil is advised for use in a Compression Ignition (C.I.) engine without major operational difficulties (Pramanik, 2003). Other publications mention much lower values for viscosity (17.1 cSt at 30 C), which would reduce the necessary blending fraction of diesel oil (Akintayo, 2004), however, conventional engines can be operated by blending biomethanol or bioethanol (with gasoline) or bio-diesel (with diesel) from 3-20%. Some report that J. curcas oil should only be used as ignition accelerator (Forson et al., 2004).
Seed cake. Like the oil, the seed cake is toxic and therefore only suitable as animal feed after processing. The toxicity of J. curcas is based on several components (phorbol esters, curcains, trypsin inhibitors and others) which make complete detoxification complicated. Detoxification has been successful at laboratory scale (Gross et al., 16 1997; Martinez Herrera et al., 2006), but since the process is complicated, it is not suitable for small scale and local use. Large scale feed production, however, has to compete on a global market with high quality demands. Therefore, detoxification must be complete, constant and guaranteed, and is thus expected to be expensive. Hence, a successful penetration of J. curcas seed cake as feed to the market at a profitable price is challenging. The main toxic, but potentially medicinal, components are phorbol esters, although in Mexico accessions without, or with low content of phorbol esters have been found (Rivera Lorca & Ku Vera, 1997; Martinez Herrera et al., 2006; Basha & Sujatha, 2007). The seed cake of this so called ‘non’ or ‘low’ toxic variety might be suitable for use as animal feed, but it still contains minor quantities of toxic components and resistance on the feed market towards this product is to be expected.
On the other hand, the seed cake is nutrient rich and therefore very suitable as fertilizer. Together with the fruit coats, the major part of the nutrients can be recycled. When no fertilizers are used, which is assumed to be the casein the use of J. curcas as a low input crop, this recycling is necessary to maintain soil fertility, especially on non fertile marginal lands. Patolia (2007a) reported total aboveground dry matter increase. Because of unavoidable inefficiencies, recycling nutrients will only be effective at a certain production level that allows a high dynamic nutrient cycle to take place. Initiating a plantation on low or non fertile soils therefore implies the need to use other fertilizers, at least at the start, to boost crop growth and seed production in the initial stages.
The by-products of J. curcas, such as fruit coats, seed hulls and the remaining de-oiled seed cake after pressing, may be used for organic fertilization, or for the production of more energy. Seed hulls can be burnt and the seed cake and fruit pulp can be used for the production of biogas by anaerobic fermentation (Lopez et al., 1997; Staubmann et al., 1997; Vyas & Singh, 2007). By burning, most nutrients will be lost, but after fermentation, most nutrients will remain in the effluent that can still be used as a fertilizer to recycle nutrients. To maintain J. curcas production at a sustainable level, it is important to be aware that a huge amount of nutrients are removed if J. curcas byproducts are exploited for additional valorization. However, the range in the reported nutrient values only comes from a few sources (Table 3), with clear variation. This indicates that environmental and management conditions have a large effect on the eventual nutrient content of the various plant parts. Soil organic matter content decreases in a production system where nutrients are removed and not replenished by fertilization.
Oil extraction. For J. curcas oil extraction at small scale, various oil presses have been developed and modified from presses for other oil seed crops. They have in common that they vary in design and are non-standardized, as they were originally developed for other (edible) seeds and need to be optimized for J. curcas seeds. Bielenberg Ram (Hand) Presses handle 7-10 kg seed h-1 and spindle presses handle 15 kg seed h-1 (Mbeza et al., 2002). Commercially available pressing systems claim processing 500 kg seed h-1 (FIG. 15).
The recoverable oil fraction is clearly affected by pressing technology. For hand powered small scale pressing (such as the Bielenberg (Hand) Ram Press), an oil yield of only 19% of the seed dry weight or 30% of the kernel was reported (Foidl & Eder, 1997; Augustus et al., 2002; Akintayo, 2004; Henning, 2004; Francis et al., 2005), which is about 60% of the total extractable amount. With mechanized pressing equipment about 75% of the oil can be recovered. Commercially available pressing systems used for large-scale de-oiling of e.g. soybean and rapeseed reach up to 90%.
Modern extraction techniques can substantially raise the extractable oil fraction. Industrial extraction with organic solvents (mainly hexane) yield near 100% of the oil content, while extractions on water basis can yield from 65-97% of the oil, depending on, (a.o.) the composition of the extract solvent, the acidity (pH) and the temperature of the solvent (Shah et al., 2004; Shah et al., 2005).
Toxicity of the cake. A wide variation in toxic, but potentially medicinal, constituents, e.g. trypsin inhibitor in defatted kernels (18.4-27.5 mg g-1; Makkar et al., 1997) was observed, as well as a wide variation in saponins (1.8-3.4%; Makkar et al., 1997) and phytate (6.2-10.1%; Makkar et al., 1997). Phorbol esters are predominantly present, but are sometimes at low levels or not detected in provenances from Mexico. Phorbol ester content ranged from 0.87-3.32 mg g-1 of kernel weight in 17 provenances (Makkar et al., 1997; 3.85 mg g-1: Martinez Herrera et al., 2006).
Much attention to various aspects and tests of toxic components (phorbol esters and curcain) in J. curcas was reported at the ‘Jatropha 97’ Symposium in Managua, Nicaragua (Chapter 4 in Gübitz et al., 1997), including experiences for using proteins from toxic and ‘low toxic’ J. curcas seeds for livestock feed (Makkar & Becker, 1997). Toxic constituents were found to be effective against a wide variety of pests (Solsoloy & Solsoloy, 1997; Rug & Ruppel, 2000). A 100% mortality rate was obtained against mosquito (Culex quinque fasciatus Say), when petroleum extracts of J. curcas leaves were used as a larvicide (Karmegam et al., 1997). The toxicity of J. curcas is based on several components (phorbol esters, curcains, trypsin inhibitors and others) that are present in considerable amounts in all plant components (including the oil), which make complete detoxification a complicated process.
Since the detoxification of J. curcas organic material is such a complicated process, it has—so far—only been successful at laboratory scale, and seems not to be suitable for small scale and local application. Like other J. curcas plant components, the seed cake is toxic and the prospect for successful penetration of the feed market with a detoxified product is challenging. The seed cake (either as remainder of the pressing process, or as a complete meal) is nutrient rich and therefore very suitable as fertilizer.
Phorbol esters of J. curcas decompose quickly as they are very sensitive to elevated temperatures, light and atmospheric oxygen (NIH, 2007); they decompose completely within 6 days (Rug & Ruppel, 2000).
To maintain J. curcas production at a sustainable level, it is important to take notion of the huge amount of nutrients that are removed from the soil if J. curcas by-products are exploited for additional uses, including the bio-refinery concept.